1. Field of the Invention
The present invention relates to a method of preventing twisting of a fusion-spliced, tube-removed fiber portion in the process of encasing the fiber portion, in a coil form, in a casing.
2. Description of the Related Art
In a conventional process of fusion-splicing a pair of optical fiber cords, first, the protective tubes of the fiber cords are removed over a predetermined length, generally, 1 meter, from the ends of the fibers, which are to be fusion-spliced. Next, the coating layers of the fibers are stripped off over a predetermined length from the ends of the fibers, which are fusion-spliced. Thereafter, the coating layer stripped fiber portions are disposed on a pair of supporting members of a fusion splicing apparatus, with the fiber ends facing to one another. Thereafter, the fibers are moved to contact each other, while applied with arc discharge to the fiber ends, so that the fibers are fusion spliced. However, there is a case where the cores of the fibers are in misalignment. In another case, the fusion-spliced portion does not have sufficient mechanical strength. In such cases, the operator removes the fibers from the supporting members and cuts off the tip portions of the fibers by a predetermined length, generally, 35 mm, from the fusion-spliced portion. The fibers are again subjected to the above processes. This sequence is repeated until a good fusion-splicing is obtained. Taking into consideration a case where such a defective fusion-splicing may occur several times, the length of the portion of each of the fibers where the protective tube is removed is generally set to about 1 meter. This portion of the fiber is referred to as "tube removed fiber portion".
When a good fusion-splicing is once obtained, the fusion-spliced fiber comprising the tube-removed fiber portions 16.sub.1 and 16.sub.2 is removed from the fusion-splicing apparatus, and put into a casing 14 to be held therein, as shown in FIG. 1A. Specifically, referring to FIG. 1A, the fusion-spliced portion 12 of the fusion-spliced fiber is fixed in a casing 14 as shown in FIG. 1A. Thereafter, the tube-removed fiber portions 16.sub.1 and 16.sub.2 of the fusion-spliced fiber are coiled as illustrated in FIGS. 1A and 1B. Next, a cover (not shown) of the casing 14 is closed to seal therein the fiber portion 16.sub.1 and 16.sub.2.
It is observed that coiling confronts subsequent twisting, and that the degree of twisting grows as the number of turns increases. As shown in FIG. 1A, the initial turn of coiling entails twisting with the upper fiber portion, for example, 16.sub.1 at an intersection of the fiber portions 16.sub.1 and 16.sub.2, and further twisting emerge with every other turn of even numbers. It is likewise observed that the initial turn of coiling does not give rise to twisting with the lower fiber portion, for example, 16.sub.2 but subsequent turns of the odd numbers after the third bring about twisting each.
The tube-removed fiber portions 16.sub.1 and 16.sub.2 are each generally coiled in the form of a 3-turn. In such a case, the twisting occurring is as intensive as not negligible with regard to optical characteristics, thereby inflicting the fibers some loss of optical transmission. It must also be noted that the optical fiber interfere with deformation of the cable due to twisting, whereby resulting in causing ease for the coiled optical fiber to spring up, getting out of the casing, with safe workability to encase a coiled optical fiber and close a casing cover subsequently thus lessened.